1. Field of the Invention
The invention relates to a transparent soap bar of exceptional clarity.
2. The Prior Art
Toilet soap is a mixture of long chain fatty acid salts and solvent, normally water, which together form three phases: solid crystal, liquid crystal and solution. Opacity as found with most soap bars results from the scattering of light at the interfaces between the several phase domains. In particular, the presence of many small solid crystals within the amorphous continuum of a toilet bar causes incident light to pass through many interfaces. Since the several phases have different refractive indices, light will be scattered rather than pass through the bar. It should be noted that the solid crystals are by nature anisotropic. They have a refractive index that is dependent upon orientation. Consequently, the refractive index of the liquid phases cannot be simultaneously matched to the refractive indices of all orientations of the solid crystals.
One approach to improve the transparency of toilet soap is to reduce the size of the solid crystals. Reduction minimizes or even eliminates light scattering due to these crystals. For instance, U.S. Pat. No. 4,517,107 (Clarke et al.) reports a soap-containing formulation becoming transparent through shear working between two mutually displaceable surfaces in an apparatus known as a cavity transfer mixer.
Solid crystals have also been avoided by crystallizing the soap mixture from a solution containing an evaporatable solvent such as ethanol. The procedure results in limiting the size of any solid crystals that might form. Illustrative in U.S. Pat. No. 4,504,433 (Inui et al.) wherein tallow/palm oil was saponified with aqueous sodium hydroxide in the presence of 20% ethanol. To the combination was added white sugar, polyethylene glycol and glycerine which resultant composition was poured into casts for cooling and drying. The presence of sugar served to match the refractive indices of the several phases and to produce a transparent bar.
Another approach is that described by U.S. Pat. No. 3,926,828 (O'Neill et al.) which indicates that saturated free fatty acids of branched chain structure provide the key to obtaining soap bars that retain transparency and initial glossy appearance after repeated usage. The O'Neill composition is typical of bars containing free triethanolamine.
U.S. Pat. No. 2,820,768 (Fromont) is the classic transparent soap bar disclosure first coining the term "neutrogenous" indicating the presence of a substantial quantity acid neutralizing material, i.e., triethanolamine. The resultant bars contain a mixture of 35-40% each of sodium and triethanolamonium soaps including substantial amounts of free triethanolamine. Starting fats and oils are reported to preferably contain 30% castor oil for improving transparency and ricinoleates, derived from saponified castor oil, as aids for dissolving higher fatty acid salts. The ricinoleates are said to inhibit crystallization of the higher fatty acid salts inside the final soap on cooling. It should be noted that ricinoleates and castor oil are expensive components desirably absent from soap products for cost reasons.
U.S. Pat. No. 4,206,069 (Borrello) note the cost problems and further indicates stickiness difficulties with prior art transparent bars. Under high humidity, it was recognized that known transparent bars are substantially hygroscopic whereupon transparency becomes lost. The patent suggests incorporating 10 to 65% of certain synthetic detergent components to harden the bar, reduce cost and improve transparency. Mixtures of sodium and triethanolammonium soaps are combined with the synthetic detergent. Included therein must be 10 to 45% of a non-volatile solvent such as an alkylene glycol or triethanolamine.
An approach combining the "neutrogenous" idea with physical shearing is found in U.S. Pat. No. 4,474,683 and U.S. Pat. No. 4,397,760, both to Story et al. Therein, a fatty acid mixture including glycerine and triethanolamine is combined with a caustic soda mixture in an intensive countercurrent mixing process providing vigorous shear. The resultant soap was said to be slightly filmy but became virtually crystal clear when wet. The bar was said to contain a mixture of sodium and triethanolamine (TEA) soaps in an amount of 30.5 and 25.9%, respectively; there was also stated to be 22.1% free TEA and 6.3% water present.
Many of the prior art bars, especially those produced by the "neutrogenous" triethanolamine type processes, have substantial color problems. Although transparent, most of the known materials survive processing in the form of a dark brown color. U.S. Pat. No. 4,468,338 (Lindberg) notes such difficulty with respect to mixed sodium and triethanolammonium fatty acid soaps. Additives such as combinations of citrate and alkali metal metabisulfite must be incorporated therein to control darkening and loss of transparency.
It is, therefore, an object of the present invention to provide a transparent soap bar of substantially improved clarify, such clarity being maintained during use of the bar.
It is another object of the present invention to provide a soap bar not requiring expensive fats and oils such as castor oil and ricinoleates to obtain adequate clarity.
It is a further object of the present invention to provide a transparent soap bar substantially less colored than that described by the prior art.
Finally, it is an object of the present invention to provide a transparent soap bar of improved hardness which avoids the stickiness associated with previously known bars.
Other objects and advantages will be discussed in the further description of the present invention.